Electro-optic sensor systems use a window or dome to separate sensitive internal mechanisms from ambient conditions. In high-speed operations, impact of soft and hard particles such as rain, sand, hail, dust, etc. can degrade the optical transmission capabilities of the window or dome. As such, some past efforts have concentrated on developing protective coatings for the windows or domes. In general, the coatings must exhibit high fracture-toughness or strength with a high elastic modulus to reduce the strain induced in the coated substrate or a low elastic modulus to absorb the impact stress.
Certain polymers, copolymers, and terpolymers have proved to be highly effective coatings while still providing for high optic transmission in the infrared wavelength region, particularly the 8-12 micrometer region. The polymers, copolymers, and terpolymers that exhibit high transparency in the 8-12 micrometer wavelength range are, by way of example and not limitation, polyethylene, ethylene-octene copolymer, polyvinylpyrrolidone, poly(acenaphthylene), styrene/ethylene-butylene copolymer, poly(1-butene), poly(acrylic acid, ammonium salt), polyamide resin, ethylene/propylene copolymer and ethylene/propylene/diene terpolymer. Each of these materials is effective as particle impact and erosion resistant coatings for infrared transmissive windows and domes.
The polymers, copolymers, and terpolymers mentioned previously have also been strengthened greatly by using these materials to form a molecular weave polymeric material as described in U.S. patent application Ser. No. 08/241,218 entitled High-Strength, High-Modulus Continuous Polymeric Material for Durable Impact-Resistant Applications, the disclosure of which has been previously incorporated herein by reference. As described in this reference, the polymeric material can be greatly strengthened by weaving fibers of the material into a woven matrix and then heating the polymeric fabric to create a consolidated molecular weave polymeric material.
Although the polymeric materials have been used successfully as coatings for electro-optical windows and domes, the electro-optic systems still exhibit a very high cost due to the cost of the substrates coated by the polymeric materials.